Plasma functionalization for cyclic transition between neutral and charged excitons in monolayer MoS2.

Y. Kim,S. Lee,Y. M. Jhon,Y. I. Jhon,J. Park,C. Kim

doi:10.1038/srep21405

Abstract

Monolayer MoS2 (1L-MoS2) has photoluminescence (PL) properties that can greatly vary via transition between neutral and charged exciton PLs depending on carrier density. Here, for the first time, we present a chemical doping method for reversible transition between neutral and charged excitons of 1L-MoS2 using chlorine-hydrogen-based plasma functionalization. The PL of 1L-MoS2 is drastically increased by p-type chlorine plasma doping in which its intensity is easily tuned by controlling the plasma treatment duration. We find that despite their strong adhesion, a post hydrogen plasma treatment can very effectively dedope chlorine adatoms in a controllable way while maintaining robust structural integrity, which enables well-defined reversible PL control of 1L-MoS2. After exhaustive chlorine dedoping, the hydrogen plasma process induces n-type doping of 1L-MoS2, degrading the PL further, which can also be recovered by subsequent chlorine plasma treatment, extending the range of tunable PL into a bidirectional regime. This cyclically-tunable carrier doping method can be usefully employed in fabricating highly-tunable n- and p-type domains in monolayer transition-metal dichalcogenides suitable for two-dimensional electro-optic modulators, on-chip lasers, and spin- and valley-polarized light-emitting diodes.

Highlights

Mauri et al suggested the use of solution-based chemical doping as an efficient and convenient means to control the PL properties of 1L-MoS219
The X-ray photoelectron spectroscopy (XPS) measurements indicate that it is a consequence of efficient dedoping of chlorine adatoms in which the dedoping level can be controlled by regulating the hydrogen plasma treatment time
The number of layers of MoS2 is determined by atomic force microscopy (AFM) (Fig. 1a)

Summary

Introduction

Mauri et al suggested the use of solution-based chemical doping as an efficient and convenient means to control the PL properties of 1L-MoS219. They showed that the PL intensity of 1L-MoS2 can increase or decrease depending on whether p-type dopants of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), or n-type dopants of nicotinamide adenine dinucleotide (NADH) cover the surface. After complete elimination of chlorine atoms, this hydrogen plasma treatment leads to n-type doping of 1L-MoS2, decreasing the PL intensity further below the luminescence level of as-prepared 1L-MoS2. Density functional theory (DFT) calculations show that despite the strong adhesion of the chlorine (or hydrogen) atoms, hydrogen (or chlorine)-plasma-assisted chlorine (or hydrogen)-dedoping reaction readily occurs with a negligible energy barrier and a large negative reaction energy that is 2 to 3 times as large as the adsorption energy of the chlorine (or hydrogen) atoms

Methods

Results

Conclusion